1. Field of the Invention
The present invention relates to the manufacturing of decorative surfaces using inkjet technology.
2. Description of the Related Art
Gravure, offset and flexography are being increasingly replaced for different applications by industrial inkjet printing systems, which have now proven their flexibility in use, such as variable data printing making short production runs and personalized products possible, and their enhanced reliability, allowing incorporation into production lines.
Inkjet technology has also caught the attention of manufacturers of decorative surfaces, such as laminate floors, which currently employ rotogravure printing on porous décor paper with ink having a viscosity at 25° C. of 1 to 2 Pa·s. The printed décor paper is then impregnated with a thermosetting resin and together with a MDF or HDF board as core layer heat pressed into a decorative panel. A manufacturing method of such decorative surfaces using inkjet printing instead of gravure printing is disclosed by EP 2293947 A (HUELSTA), however no specific inkjet inks are disclosed.
For achieving high productivity, single pass inkjet printing using page wide print heads or page wide staggered print heads is the preferred option. However, it is then necessary to have an extremely high inkjet printing reliability, since a single failing nozzle creates a line defect in the printed image.
Many factors control the reliability of a print head during use. They are print head related factors, such as the waveform and jetting conditions like drop velocity and frequency, or otherwise ink related factors such as the components and the physical properties of the ink.
Aqueous inkjet ink sets for single pass printing are disclosed in EP 2535382 A (FUJIFILM), EP 2535380 A (FUJIFILM), EP 2412766 A (FUJIFILM), US 2009196995 (FUJIFILM), WO 2006/012142 (DU PONT), EP 1744897 A (DU PONT), US 2005140763 (DU PONT), EP 1338632 A (KODAK).
An important factor for single pass inkjet printing is latency. Latency is the ability of an inkjet ink to print correctly after sitting idle in a print head for a period of time. Poor latency is often caused by the drying of the ink in the print head. Improvements in latency has been accomplished by including a block polymer and a polymer latex, as for example disclosed by US 2012075381 (FUJIFILM), or by including specific humectants, as for example disclosed by US 2008060548 (DU PONT).
Also extra constraints are put on the ink set by the requirements for decoration, such as light fastness and metamerism. Metamerism is a phenomenon which occurs when two materials match in colour under some lighting conditions but not under other lighting conditions. A customer expects all parts of e.g. a kitchen cabinet that have the same colour to match whether viewed in daylight, under an incandescent light bulb or under halogen lighting. The selection of the pigments in the different inkjet inks plays an important role for metamerism. EP 1966332 A (HP) discloses an inkjet ink set exhibiting good metamerism, which includes a neutral black ink comprising an ink vehicle, and a black pigment (K), cyan pigment (C), and violet pigment (V); and a yellow ink comprising an ink vehicle and a yellow pigment having comparable lightfastness as the neutral black ink. Metamerism can also be improved by using additional inkjet inks in the ink set. EP 1489150 A (SEIKO EPSON) discloses that metamerism is improved by using an inkjet ink set including a yellow ink, a magenta ink, a cyan ink, a red ink, and optionally a black ink.
In manufacturing methods of decorative surfaces, there is still a need for improved inkjet technology having high printing reliability and high productivity.